In recent years, there is a technology for mixing an expensive, rare metal, such as indium, in a thin film formed on the surface of a glass plate to provide a function of cutting off (shielding) infrared rays (for example, see the pamphlet of PCT International Patent Publication No. 2004/011381 and the pamphlet of PCT International Patent Publication No. 2005/095298).
As to the infrared shielding glass described in the pamphlet of PCT International Patent Publication No. 2004/011381, use of fluorine component-containing ITO powder having excellent heat resistance allows a sol-gel method to be performed even at high temperatures of 350° C. or higher. The fluorine component with the ITO particles insulated from heat is introduced into an infrared cutoff film.
In the infrared shielding glass described in the pamphlet of PCT International Patent Publication No. 2005/095298, an infrared cutoff film is formed on at least one of the surfaces thereof. The infrared cutoff film is an organic-inorganic composite film obtained by compositing an organic substance and an inorganic oxide, in which ITO fine particles are contained as an infrared cutoff component.
As a method for forming a thin film, such as an infrared cutoff film, on the surface of a glass plate, flow coating method has been known. In the flow coating method, as shown in FIG. 6, with a glass plate 11 held by a glass plate holding member 14 in the vertical direction, a nozzle 12 is used to eject infrared cutoff liquid 13 onto the upper portion of the glass plate 11. The infrared cutoff liquid 13 ejected onto the upper portion of the glass plate 11 flows vertically downward, and is applied onto the glass plate 11 (see Japanese Laid-Open Patent Publication (Kokai) No. 7-157749).
In the flow coating method shown in FIG. 6, however, the infrared cutoff liquid 13 ejected onto the upper portion of the glass plate 11 flows vertically downward and is applied onto the glass plate 11, so that the film thickness of the infrared cutoff film on the upper portion of the glass plate 11 is smaller than the film thickness of the infrared cutoff film on the lower portion of the glass plate 11. As a result, the infrared cutoff effect of the upper portion of the glass plate 11 is weaker than the infrared cutoff effect of the lower portion of the glass plate 11. When the glass plate 11 is installed in a vehicle in such a way that the upper portion of the glass plate 11, where the infrared cutoff effect is weaker, is located on the upper side of the vehicle window pane, a large amount of infrared rays, especially light having a wavelength of 1550 nm, enter the vehicle as shown in FIG. 7, which causes burning sensation of the skin of a passenger in the vehicle.
Increasing the amount of ejection of the infrared cutoff liquid 13 to increase the film thickness of the whole infrared cutoff film so as to enhance the infrared cutoff effect disadvantageously increases the cost of manufacturing the infrared shielding glass.
It is an object of the present invention to provide a vehicle window pane that can be manufactured at low cost and can reduce burning sensation of the skin of a passenger in the vehicle, and a manufacturing method therefor.